This invention concerns a device for applying straightening force to flexible tubular structures, particularly extended medical instruments such as fiberscopes, fiber optic colonoscopes and remote controlled biopsy tools, whereby the instrument, particularly the highly flexible leading end thereof, can be selectively straightened in a very accurate manner and to various degrees for straightening surrounding twisted or tortuous body passages or conduit for advancing the instrument therethrough.
Such medical instruments are described in the Olympus Optical Co., Ltd. (Olympus Tokyo) instructional manual entitled "Olympus CF type 10L/I/M" incorporated herein by reference.
In general, these endoscopic instruments must be quite flexible, even floppy, especially at the distal end, in order to follow rather than prod the sensitive and rupturable tissue of the stomach, esophagus, intestines or the like. Often, however, a deep insertion such as is common in colonoscopy will encounter twisted or severely bent body conduit which must be brought to a straighter condition to allow advancement of the instrument therethrough.
Stiffening devices have been proposed for insertion into an accessory channel or tubular passage in such endoscopic instruments in order to reduce the flexibility thereof. Such devices are shown in U.S. Pat. Nos. 3,854,473 and 4,215,703, the disclosures of which are incorporated herein by reference, and employ an elongated coiled wire compression spring or closely wound helix, axially positioned in the endoscope, wherein the spring rigidity and hence the endoscope stiffness is controlled by adjusting the spacing between the spring coils helical windings. Such a compression of the 3,854,473, however, does not afford the real straightening force necessary for actually straightening the endoscope, particularly its floopy distal leading end, and the adjacent and more difficult body conduit portions, while also providing, upon demand, the necessary flexibility for following normal contours, without excessive prodding or thrusting particularly where easily rupturable tissue is involved. Likewise, the handle structure of the 4,215,703 patent necessarily imparts very undesirable rotation to the inner core and outer coil when applying tension to the core. Such rotation can defeat the purpose of the stiffener, the degree of tension, l.e. the heavy tension considered necessary by applicant is not readily achievable by the handle structure of this patent.
A principal object of the present invention therefore is to provide a means for applying accurate straightening force to endoscopic or other such intruments over an extremely wide range of straightening force in order to accommodate practically all insertion situations encountered in the use of such instruments.